Host-plant diversity of the European corn borer Ostrinia nubilalis: what value for sustainable transgenic insecticidal Bt maize?

The strategies proposed for delaying the development of resistance to the B acillus thuringiensis toxins produced by transgenic maize require high leve ls of gene flow between individuals feeding on transgenic and refuge plants . The European corn borer Ostrinia nubilalis (Hubner) may be found on sever al host plants, which may act as natural refuges. The genetic variability o f samples collected on sagebrush (Artemisia sp.), hop (Humulus lupulus L.) and maize (Zea mays L.) was studied by comparing the allozyme frequencies f or six polymorphic loci. We found a high level of gene flow within and betw een samples collected on the same host plant. The level of gene flow betwee n the sagebrush and hop insect samples appeared to be sufficiently high for these populations to be considered a single genetic panmictic unit. Conver sely the samples collected on maize were genetically different from those c ollected on sagebrush and hop. Three of the six loci considered displayed g reater between-host-plant than within-host-plant differentiation in compari sons of the group of samples collected on sagebrush or hop with the group o f samples collected on maize. This indicates that either there is genetic i solation of the insects feeding on maize or that there is host-plant diverg ent selection at these three loci or at linked loci. These results have imp ortant implications for the potential sustainability of transgenic insectic idal maize.